Datasheet

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SBOS266E − JUNE 2003 − REVISED AUGUST 2008
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14
APPLICATIONS INFORMATION
WIDEBAND VOLTAGE-FEEDBACK
OPERATION
The OPA832 is a fixed-gain, high-speed, voltage-
feedback op amp designed for single-supply operation
(+3V to +10V). It features internal R
F
and R
G
resistors
which make it easy to select a gain of +2, +1, and −1
without external resistors.The input stage supports in-
put voltages below ground and to within 1.7V of the pos-
itive supply. The complementary common-emitter out-
put stage provides an output swing to within 25mV of
either supply pin. The OPA832 is compensated to pro-
vide stable operation with a wide range of resistive
loads.
Figure 1 shows the AC-coupled, gain of +2 configura-
tion used for the +5V Specifications and Typical Char-
acteristic Curves. The input impedance matching resis-
tor (66.5Ω) used for testing is adjusted to give a 50Ω
input match when the parallel combination of the bias-
ing divider network is included. Voltage swings reported
in the Electrical Characteristics are taken directly at the
input and output pins. For the circuit of Figure 1, the to-
tal effective load on the output at high frequencies is
150Ω || 800Ω. The 332Ω and 499Ω resistors at the non-
inverting input provide the common-mode bias voltage.
Their parallel combination equals the DC resistance at
the inverting input (R
F
 R
G
), reducing the DC output
offset due to input bias current.
OPA832
V
S
=+5V
V
OUT
66.5Ω
V
IN
499Ω
V
CM
=2V
332Ω
R
L
150Ω
V
CM
=2V
V
CM
=2V
6.8µF
+
0.1µF
0.1µF
R
F
400Ω
R
G
400Ω
Figure 1. AC-Coupled, G = +2, +5V Single-Supply
Specification and Test Circuit
Figure 2 shows the AC-coupled, gain of +2 configura-
tion used for the +3.3V Specifications and Typical Char-
acteristic Curves. The input impedance matching resis-
tor (66.5Ω) used for testing is adjusted to give a 50Ω
input match when the parallel combination of the bias-
ing divider network is included. Voltage swings reported
in the Electrical Characteristics are taken directly at the
input and output pins. For the circuit of Figure 2, the to-
tal effective load on the output at high frequencies is
150Ω || 800Ω. The 887Ω and 258Ω resistors at the non-
inverting input provide the common-mode bias voltage.
Their parallel combination equals the DC resistance at
the inverting input (R
F
 R
G
), reducing the DC output
offset due to input bias current.
OPA832
V
S
= +3.3V
V
OUT
66.5Ω
V
IN
887Ω
V
CM
= 0.75V
258Ω
R
L
150
Ω
V
CM
=0.75V
V
CM
=0.75V
6.8
µ
F
+
0.1µF
0.1µF
R
F
400
Ω
R
G
400
Ω
Figure 2. AC-Coupled, G = +2, +3.3V
Single-Supply Specification and Test Circuit
Figure 3 shows the DC-coupled, gain of +2, dual power-
supply circuit configuration used as the basis of the ±5V
Electrical Characteristics and Typical Characteristics.
For test purposes, the input impedance is set to 50Ω
with a resistor to ground and the output impedance is
set to 150Ω with a series output resistor. Voltage swings
reported in the specifications are taken directly at the in-
put and output pins. For the circuit of Figure 3, the total
effective load will be 150Ω || 800Ω. Two optional compo-
nents are included in Figure 3. An additional resistor
(175Ω) is included in series with the noninverting input.
Combined with the 25Ω DC source resistance looking
back towards the signal generator, this gives an input
bias current cancelling resistance that matches the
200Ω source resistance seen at the inverting input (see
the DC Accuracy and Offset Control section). In addi-
tion to the usual power-supply decoupling capacitors to
ground, a 0.01µF capacitor is included between the two
power-supply pins. In practical PC board layouts, this
optional capacitor will typically improve the 2nd-har-
monic distortion performance by 3dB to 6dB.